This disclosure relates to an induction or electrodeless high intensity discharge (HID) lamp assembly, and more particularly is directed to an optical assembly for providing a preferred distribution of light output.
In general, optical solutions for light sources must address a myriad of issues. Among these issues is collecting as large a percentage as possible of the light output from the lamp for a particular use. Since the induction HID lamp employs a coil disposed around a zone of the arctube body, the light optics must also address potential light blockage by the coil, be flexible relative to coil geometry and location, and allow for high coil coupling efficiency and high optical efficiency irrespective of the optical design. In traditional HID light sources, such as quartz metal halide (QMH), ceramic metal halide (CMH), or high-pressure sodium (HPS) lamps, the light output is generally in the horizontal or equatorial plane. In the induction HID lamp, light output is generally in the vertical plane, along the apex and nadir of the lighting system. This requires highly specific optical solutions to address potentially high on-axis light directly below the lighting system, which would result in a non-uniform illumination pattern.
Still another issue relates to providing a preferred distribution of light output intensity for coupling into a wide variety of applications. Thus, providing high collection efficiency and providing a light output intensity distribution that is suitable for specific lighting applications is desirable.
Since the induction HID lamp employs an arctube body that is a pressurized vessel, and because of the electromagnetic field associated with operation of this type of lamp, there are additional considerations relating to containment of non-passive failures, shielding against electromagnetic interference, and UV filtering. Incorporating these various needs into the optics is desired, as well as a simple solution that adequately addresses each without adding undue complexity to the geometry of the optics. In one example application of HID lamps, a quartz metal halide light source is associated with large area lighting from extended heights. For example, quartz metal halide light sources are often used to provide parking lot illumination. The lamp is typically mounted at a substantial height at the top of a pole on the order of thirty feet (30′). Moreover, a goal or objective of the light assembly and particularly the optics is to cover a ground footprint of approximately one hundred twenty feet by one hundred twenty feet (120′×120′). There is an additional challenge to provide suitable optics that will illuminate this ground area as uniformly as possible. This illumination can be characterized by a ratio of the maximum illuminance level within the ground footprint divided by the minimum illuminance level within the ground footprint. For traditional HID lighting systems, this ratio is on average 6:1 and at best 3:1. Illumination design takes both the max:min ratio and the minimum illuminance into account. Minimum illuminance levels are required for safety and appearance purposes. Therefore, a low max:min ratio along with a high minimum illuminance level is desired to efficiently illuminate ground applications with the smallest amount of light flux necessary. As will be appreciated, a large amount of the light will have the tendency to illuminate the area directly adjacent the pole, while the challenge is to direct zones of the light output to the more remote areas of the illuminated region and in a generally uniform and highly efficient manner.
The compactness and weight of the electrodeless or induction HID lamp assembly are two key features that require improvement in existing lamp assemblies. By way of example only, approximately three-fourths of the total price of these types of light assemblies is associated with the pole on which the light assembly is mounted. Therefore, being able to decrease the weight of the lamp assembly, and providing a more compact unit that reduces the cross-sectional area of the lamp assembly exposed to the external environment, allows less impact by the wind, lower light system weight, and use of a lighter pole. Dramatic savings could potentially be achieved.
In a second example application of HID lamps, a quartz metal halide light source is associated with spot and flood lighting in sporting arenas or stadia from extended heights. The lamp is typically mounted at a substantial height above the arena or stadium, typically about 100′ or more above the lighted surface. In order to provide the preferred distribution of illumination on the lighted surface, each of a large number of light sources is aimed to illuminate a subsection of the total illuminated area. Due to the very long distances over which the light is projected, the angle of each beam of light, and the distribution of light intensity within each beam must be very well controlled. This beam can be characterized by the beam width, typically defined as the full-width at half-maximum (FWHM) of the light intensity distribution in the optical far field. In such applications, the same advantages of the compactness and weight of the induction HID lamp assembly are two key features that enable simpler, lighter, smaller, more efficient, more effective, and less expensive lighting installations than those presently in use.
The induction HID lamp arctube body may be made of quartz, which has limitations in maximum overall wattage, life, and luminous output. Preferably, the lamp arctube body is made of a ceramic material, such as polycrystalline alumina, which will increase the life and luminous output of the lamp, while provide a smaller light source with a more uniform intensity output compared to a quartz lamp.
Accordingly, a need exists for an optical arrangement that adds additional value to the use of induction HID lamps.